FIG. 11 shows an example of a conventional sealing device of this type. The reference numeral 100 generally indicates the device shown, which comprises a first annular seal member 102 fitted onto a rotating shaft 101 that is schematically shown and a second annular seal member 104 fitted in the inner periphery of an axle hole 103a of a housing 103. Provided between the first seal member 102 and the second seal member 104 are a main seal portion 105 for sealing up an object of sealing 0 which consists, e.g., of oil, and an auxiliary seal portion 106 for preventing foreign matter, such as external contaminants, from intruding into this main seal portion 105. Employed in this auxiliary seal portion 106 is a seal lip 107, which is a contact-type seal adapted to be in sliding contact with the associated sliding surface.
The above-described prior-art device, however, has the following problem, which is due to the employment of the seal lip 107 in the auxiliary seal portion 106.
First, under a high-speed rotating condition, the heat generation due to the sliding friction of the seal lip 107 becomes excessive, with the result that the material of the seal lip 107, which consists, e.g., of rubber, deteriorates, which leads to a premature failure such as seal leakage.
Second, due to the presence of the seal lip 107, the cavity portion 108 between the auxiliary seal portion 106 and the main seal portion 105 exists as a sealed space with poor permeability. As a result, moisture condenses in this cavity portion 108, which may cause corrosion, etc. of the metal portions.
In view of this, a non-contact seal, such as a labyrinth seal, might be used in the auxiliary seal portion 106, as shown in FIG. 12. However, though it can reduce the intrusion of external contaminants, a non-contact seal will deteriorate extremely in sealing performance if the gap thereof is too large, so that the size of the gap must inevitably be limited. Further, in use, such a unitized device must be able to tolerate any change in the assembly condition on the side of the user, i.e., a dynamic eccentricity, such as a precessional movement or an offset between the rotating shaft 101 and the axle hole 103a. Thus, in the case where a non-contact-type seal is used in the structure of the auxiliary seal portion 106, there are two requirements, which it has been impossible to satisfy at the same time. That is, the gap must be made small in order to ensure the sealing property, whereas it must be made large in order to tolerate a dynamic eccentricity.
Further, in such a unitized sealing device, there is provided between the first seal member 102 and the second seal member 104 a buffer portion 109 for buffering the axial load generated when mounting the rotating shaft 101 by passing it through the inner periphery of the second seal member 104.
However, the buffer portion 109 of conventional type is arranged inside the axle hole 103a of the housing 103, and has the following problems:
First, the thrust load when mounting the shaft acts directly on the abutting portions of the first and second seal members 102 and 104 through the intermediation of the buffer portion 109 as an axial load, with the result that the portions on which the load acts are deformed, which may cause the seal to become defective.
Further, there is a risk that the heat generated in this buffer portion 109 as a result of the sliding during rotation will be transmitted to the seal lip 107 to cause premature deterioration of the material, thus leading to a short service life. A buffer structure of this type is disclosed, for example, in U.S. Pat. No. 4,531,748.
The present invention has been made to solve the above problems in the prior art. It is accordingly an object of this invention to provide a unitized sealing device which employs a non-contact-type seal in the auxiliary seal portion to eliminate the problem of frictional heat generation, torque loss, etc., and, at the same time, the auxiliary seal portion of which has an enhanced foreign matter discharging ability to make it possible to improve the sealing property with respect to foreign matter while tolerating dynamic eccentricities.
Another object of this invention is to provide a unitized sealing device in which the axial load acting on the second seal member when mounting the shaft is prevented from being directly applied to the first seal member, and which can prevent the heat generated in the buffer portion as a result of the sliding during rotation from being transmitted to the seal portions.